Work on the basophil system was continued with the development of a new theory of the kinetics of activation and specific desensitization of cells from allergic and immunized individuals. The theory has been applied to the analysis of a wide variety of data. We also developed new methods, based on measurements of the kinetics of cell activation for determining whether or not descending limb of biphasic dose response curve falls because of insufficient cross-linking. We studied equilibrium and kinetic properties of IgG oligomers of defined size interacting with Fc receptors on a macrophage-like cell line. The results of the equilibrium studies provided the first experimental evidence in support of our predictions that receptor cross-linking can lead to non linear Scatchard plots. In addition, the data suggested two different types of binding sites for dimeric and trimeric oligomers, but only a single type for monomers. The maximum affinity enhancements -- 200 for dimeric relative to nonomeric and 2.5 for trimeric relative to dimeric, indicate considerable strain or large differences in the entropic parts of the equilibrium constants for solution phase as opposed to cell surface reactions. The dissociation kinetics of dimer and trimer were biphasic and the rate of dissociation was accelerated by high concentrations of monomer.